Conventionally, known is the detection of vibration of a vibrating member of a musical instrument. In a piano, a string vibrates as a result of being played, and this is accompanied by vibration of a vibrating member such as a soundboard for example. In order to record and later play back the playing of a piano, a sensor is arranged in the piano, and vibration of the vibrating member is detected by the sensor. In Patent Document 1 described below, a vibration sensor is installed on a soundboard, and a vibration waveform is detected by the sensor. The soundboard mainly vibrates such that a direction perpendicular to the plane thereof is a main vibration direction. Consequently, in Patent Document 1 described below, vibration in the main vibration direction of the soundboard is mainly detected.
However, a soundboard vibrates not just in a main vibration direction, but also in a plane direction perpendicular to the main vibration direction for example. The synthesis of complex vibration in three axis directions gives rich acoustics. Consequently, if sound that is true to an original sound is to be reproduced, it is preferable to detect not just vibration in a main vibration direction, but also vibrations in a plane direction. In a case where a sensor for detecting vibration in three axis directions is to be installed in an existing acoustic piano, the use of a three-axis sensor represented by Patent Document 2 described below can be considered for example.